The present invention relates generally to laser cutting probes for use in surgical procedures. More particularly, this invention pertains to a solid-state erbium laser surgical cutting probe and system for use in surgical procedures requiring high precision, including intraocular surgical procedures such as retinotomy, vitrectomy, retinectomy, capsulotomy, sclerostomy, and goniotomy.
Laser cutting, ablation and vaporization are common techniques in surgery. For example, the CO2 laser has been used in dermatology for cutting tumors. Corneal cutting and reshaping is being performed with excimer photorefractive surgery (PRK). The best laser wavelength for many procedures is the wavelength having the highest absorption in tissue. Because water comprises the highest component of the tissue, the best water absorption wavelength often has the best cutting effect.
The most commonly used lasers for cutting are CO2 laser at 10.6 xcexcm (water absorption coefficient=8.5xc3x97102/cmxe2x88x921), and Er:YAG at 2.94 xcexcm, (water absorption coefficient=1.3xc3x97104/cmxe2x88x921).
Intraocular cutting techniques are needed for ophthalmic surgery. Laser intraocular cutting may improve the surgery with smaller incisions, easier control, and higher precision. Several studies have tried different lasers and various delivery devices to develop this technique.
Lewis A. et al. in the Hebrew University of Jerusalem, Israel, guided an excimer laser beam (193 nm) with an articulated mechanical arm and confined it with a variable-diameter tapered tube (1 mm to 125 xcexcm in diameter). An air stream was used to push the intraocular liquid out of a cannula and remove fluid from the retina surface just in front of the needle tip. With such an excimer laser delivery system, it was possible to remove retinal tissue accurately without collateral damage.
Dodick J M, et al tried to overcome the delivery problems by conducting a short pulse Nd:YAG laser (1.064 xcexcm) into the eye with a silica fiber. At the end of the surgical probe, the short pulses hit a titanium target and generated shock waves. This device was applied to fragment nuclear material for cataract extraction.
D""Amico et al delivered Er:YAG laser through a fluoride glass fiber to an endoprobe with sapphire or silica fiber tips ranging from 75 to 375 xcexcm This probe was used for transection of vitreous membranes, retinotomy, and incision and ablation of epiretinal membranes. Results showed that twenty-five vitreous membrane transections were made in 16 eyes at distances ranging from 0.5 to 4.5 mm from the retina with radiant exposures ranging from 2 to 50 J/cm2 (0.3-5.5 mJ) with nonhemorrhagic retinal damage in a single transection. Sharp, linear retinotomies were created successfully in five eyes. Epiretinal membrane ablations were performed with radiant exposures ranging from 1.8 to 22.6 J/cm2 (0.3-2 mJ). In aqueous media, results of microscopic examination showed partial- to full-thickness ablation with a maximum lateral thermal damage of 50 xcexcm. In air- and perfluoro-N-octane-filled eyes, there was increased lateral damage with desiccation of residual tissue. In 12 aqueous-filled eyes, 18 linear incisions were successfully performed, with retinal nonhemorrhagic damage in 2 eyes and hemorrhage in 5. Based on these results, a commercial florid glass delivered Er:YAG laser has been developed for further research (VersaPulse(copyright)Select(trademark) Erbium, Coherent(trademark), Palo Alto, Calif.).
Joos K, et al delivered Er:YAG laser (2.94 xcexcm) through ZrF fiber and coupled to a short piece of sapphire fiber (Saphikon, Inc., Milford, N.H.), or low-OH silica fiber at the end of the intraocular probe. The probe was combined with an endoscope to perform goniotomy in vitro and in vivo. The results showed that minimum tissue damage created with the Er:YAG energy was at an energy level of 2 to 5 mJ per pulse.
Pulsed Er:YAG laser at 2.94 xcexcm wavelength is capable of cutting human tissue with high precision and little thermal damage to the surrounding tissue. The potential applications include photo-refractive keratectomy, plastic surgery, and intraocular cutting surgery such as retinotomy, vitrectomy, capsulotomy, goniotomy, etc.
To understand the proper use operation of a micro-Er:YAG laser in the surgical applications, it is important to understand its dynamics. The energy level scheme of a 970 nm diode pumped Er3+ in a YAG crystal is shown in FIG. 4. The 970 nm diode directly pumps the Er3+ to the upper laser energy level. The laser action occurs between the 4I11/2-4I13/2 states. Each of these states is Stark split into about 6 to 7 branch energy levels by the crystal field. These levels are thermally populated as described by a Boltzmann distribution. When the X2 branch of 4I11/2 is relatively higher populated than the Y7 branch of 4I13/2, the 2.94 xcexcm laser transition will occur, even when the entire 4I11/2 and 4I13/2 levels are not inversed. Continuous wave (CW) and quasi-cw laser operations of this transition at room-temperature have been reported with high efficiency and high output power. When the population of 4I13/2 accumulates to a certain density, two neighboring Er3+ ions can interact. One ion jumps to the higher energy 4I9/2 and the other one jumps to the lower level 4I15/2. Then the 4I9/2 level ion will relax to the upper laser level 4I11/2 by rapid multi-photon transition within about 1 xcexcs. This is called the up-conversion process. It is responsible for shortening the lifetime at the lower laser level which simultaneously leads to excitation of the upper laser level.
Since lifetime at the 4I11/2 level is shorter than at the 4I13/2 level, highly doped crystals such as YAG:Er3+ at 50% concentration have to be used to reduce the lifetime at the lower laser levels, and increase the probability of interaction at the lower level laser ions.
All commercial Er:YAG lasers presently are flash light pumped. Some of the companies which produce the Er:YAG lasers are: Big-Sky, SEO, LSD, Kigre, FOTONA, Quantex, etc. The most common feature of these lasers are: wavelengthxe2x80x942.94 xcexcm; pulse lengthxe2x80x94150 to 300 xcexcs; energy per pulsexe2x80x94100 to 1000 mJ; and repetition ratexe2x80x941 to 20 Hz.
Other manufacturers (e.g. Coherent, Premier, and Candela) produce fluoride glass delivered Er:YAG laser. Because all fluoride glass fibers can not withstand high laser power, these lasers normally have outputs of less than 20 mJ per pulse of energy.
Kigre Inc. produces a small Er:YAG laser, which places a small flash light pumped Er:YAG laser head into a pistol style hand piece. However, it requires high voltage power for the flash light and the hand piece is not small enough for intraocular surgery.
There is no commercialized diode pumped Er:YAG laser. Theoretical and preliminary experiments showed that a diode pumped Er:YAG laser has a much higher conversion efficiency (10% to 20%) than flash light pumped ones (efficiency less than 2%). Dinerman, et. al. used a 970 nm diode laser and a Ti:sapphire laser to end pump a 3 mm long Er:YAG laser. This produced 143 mW of cw power when the pump power was 718 mW. Hamilton, et. al. pumped a 2xc3x972xc3x9714 mm Er:YAG laser rod with a pulsed diode laser array bar with 200 W peak power, and reached the maximum output energy of 7.1 mJ per pulse at 100 Hz repetition rate. The parameters and results of these experiments are listed in Table I:
These results indicate that using a diode array pumped micro-Er:YAG laser is very promising for low energy requirements.
One of the biggest difficulties in the practical application of the erbium laser for such surgical applications is that none of the available fibers are ideal for the delivery of the laser. In addition to the bulky mechanical articulated arm, fiber optics available for these wavelengths are: fluoride glass fiber, single-crystal sapphire fiber, chalcogenide glass fiber, polycrystalline fiber, and hollow waveguides. Although they offer some ability to deliver different cutting wavelength, all of them have one or more defects of: brittleness, water solubility, toxicity, sensitive to UV exposure, limited mechanical strength, low temperature damage threshold, and low laser damage threshold. The articulated arms and sapphire fibers are not flexible enough for effective use by the surgeon. Although fluoride glass fibers have better flexibility, they are too brittle and their damage energy thresholds are too low for intraocular use.
What is needed, then, is a cutting probe system that is sufficiently flexible and mechanically strong to reliably deliver the energy from an erbium laser for use in intraocular surgery and in other surgical procedures requiring high precision.
The shortcomings of the prior art have been addressed in this invention by a novel micro Er:YAG laser (2.94 xcexcm) based intraocular surgical probe system.
To avoid the difficulty of fiber delivery of the erbium laser power, the system includes an erbium laser head which fits into a surgical hand piece. The output of the erbium laser from the hand piece is delivered to the surgical field by a short piece of rigid sapphire or low-OH silica fiber which forms a disposable probe tip. The erbium laser head is pumped by diode laser energy delivered by a silica fiber bundle, instead of a high voltage electric powered flash lamp, so that the hand piece is safe and easy to hold.
The probe uses a plug-in style disposable tip which is made of a short piece of silica or sapphire fiber. This probe is capable of delivering a range of 0.5-10 mJ per pulse of 2.94 xcexcm laser energy at approximately at 1-20 Hz. Accordingly, the probe and system can be used to perform vitreoretinal surgery, including retinotomy, vitrectomy, capsulotomy, goniotomy, as well as other superficial surgery where precise tissue cutting is necessary. With an enlarged erbium laser head, the cutting probe of this invention can produce enough energy to perform laser cataract removal.
The laser cutting probe and system of this invention solves the difficulty of delivering Er:YAG laser energy at 2.94 xcexcm. It renders intraocular cutting clinically possible with a laser and may be useful also in other subspecialties which need low energy levels and precise tissue cutting.